Cortical mapping helps brain tumor removal

In 2006, it was estimated that 18,820 new cases were diagnosed and 12,820 deaths were associated with malignant tumors of the brain and other parts of the central nervous system.

In brain tumor surgery, the goal is always to maximize the resection while minimizing the loss of critical neurological functions. Surgically removing brain tumors adjacent to “eloquent” or functional regions of the brain poses significant risks for causing neurological impairments. In order to minimize such risks, awake brain surgery with brain mapping has long been advocated by many neurosurgeons.

Researchers at MD Anderson Cancer Center analyzed neurological outcomes of 309 consecutive patients with brain tumors occurring near or in the eloquent cortex, the region of the brain that if disturbed, can result in loss of language skills as well as cause varying degrees of paralysis. The most common areas of eloquent cortex are in the left temporal and frontal lobes for speech and language, occipital lobes for vision, parietal lobes for sensation, and motor cortex for movement.

The results of this study, Awake Craniotomy for Brain Tumors near Eloquent Cortex: Correlation of Intraoperative Cortical Mapping with Neurological Outcome in 300 Consecutive Patients, will be presented by Stefan Kim, MD, 4:15 to 4:30 p.m. on Monday, April 16, 2007, during the 75th Annual Meeting of the American Association of Neurological Surgeons in Washington, D.C. Co-authors are Ian E. McCutcheon, MD, FRCSC, Raymond Sawaya, MD, Jeffrey S. Weinberg, MD, Frederick F. Lang, MD, Amy B. Heimberger, MD, Franco DeMonte, MD, FRCSC, Samuel J. Hassenbusch, MD, PhD, Laurence Rhines, MD, David Z. Ferson, MD, Jeffrey Wefel, PhD, Dima Suki, PhD, and Sujit S. Prabhu, MD, FRCS. This research is being honored with the Mahaley Award.

Because every individual is unique in the organization of the functional areas of his or her brain, brain mapping technique is used to establish a real-time functional map of the brain surface. The patient is awake, and a small area of the brain is stimulated with a hand-held probe that emits a small electric current. The stimulation, in essence, causes that portion of the brain to temporarily become inactivated. Any disruption of speech or motor function signifies an area that must not be disturbed during tumor removal. Thus, brain mapping delineates a safe boundary for tumor resection with maximal preservation of neurological functions. The relevancy of this technique is further corroborated by several studies that suggest the extent of tumor removal is a strong prognostic factor for patient survival. Without brain mapping, aggressive tumor removal near the functional areas may not be safely carried out.

Although many have argued that functioning brain regions must be identified and spared prior to surgical resection of the tumor, it is unclear whether a positive identification of the eloquent areas is always necessary to minimize functional impact of the surgery. In other words, if a series of stimulations of the presumed eloquent areas around the tumor margin shows no disruption of functions (meaning negative mapping) and thus no functional areas are identified before the tumor removal is undertaken, it is not clear whether this poses an increased risk for worsened neurological impairment after the surgery. This research compares the results of brain mapping with neurological outcomes to evaluate whether negative mapping adversely influences the neurological outcomes or the extent of tumor resection.

In the study, 309 brain tumor patients were clinically evaluated before undergoing surgery, immediately and one month post surgery. Craniotomy was tailored to encompass tumor plus adjacent areas presumed to contain eloquent cortex. Intraoperative cortical stimulation for language, motor, and/or sensory function was performed in all patients to safely maximize surgical resection. Sixty-five percent of patients had greater than 95 percent tumor removal, while 78 percent had greater than 85 percent tumor removal. Brain mapping results, whether the eloquent areas were identified or not, had no significant effect on the extent of resection. The following additional outcomes were noted:

• In the early post surgery period, 36 percent of patients experienced new or worse deficits.
• At one month post surgery, 84 percent of patients showed improved or stable neurological status, while only 16 percent continued to exhibit new or worse deficits.
• Eloquent areas were identified in 65 percent of patients; worsened deficits were noted in 21 percent of this group, whereas only 10 percent of patients with negative mapping showed such deficits.
• Positive brain mapping, extent of resection less than 95 percent, and presence of intraoperative neurological changes were all predictors of worsened neurological outcomes using multivariate logistic regression statistical analysis.
• Sixty-six percent of the 59 patients who underwent rigorous neuropsychological testing showed a significant decline from the baseline. The patients who had positive mapping of the eloquent areas and better preoperative test performances were more likely to evidence postoperative declines in expressive language.

“Brain mapping during awake brain surgery allows surgeons to maximize tumor resection in eloquent brain while minimizing the morbidity associated with its disturbance. This research shows that as long as the brain mapping technique is properly carried out, a negative mapping of eloquent areas appears to provide a safe margin with a lower incidence of neurological deficits, but with a comparable extent of tumor resection,” stated Dr. Kim.

“Identification of eloquent areas did not eliminate postoperative neurological deficits, most likely indicating close proximity of functional brain area to tumor. What must also be emphasized is that even when these deficits do occur, they are seldom severely debilitating. In other words, most patients who experienced worsened neurological outcome continued to maintain similar performance status before and after the surgery. This study again demonstrates the importance of brain mapping before the surgeon removes the tumor because without it, the outcome could be much more devastating to the patient,” concluded Dr. Kim.